+ function(){
  var VSHADER_SOURCE =
    'attribute vec4 a_Position;\n' +
    'uniform mat4 u_ModelMatrix;\n' +
    'void main() {\n' +
    '  gl_Position = u_ModelMatrix * a_Position;\n' +
    '}\n';

  // Fragment shader program
  var FSHADER_SOURCE =
    'void main() {\n' +
    '  gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);\n' +
    '}\n';

  // Rotation angle (degrees/second)
  var ANGLE_STEP = 45.0;

  function main() {
    if (!initShaders(gl, VSHADER_SOURCE, FSHADER_SOURCE)) {
      console.log('Failed to intialize shaders.');
      return;
    }

    // Write the positions of vertices to a vertex shader
    var n = initVertexBuffers(gl);
    if (n < 0) {
      console.log('Failed to set the positions of the vertices');
      return;
    }

    // Specify the color for clearing <canvas>
    gl.clearColor(0.0, 0.0, 0.0, 1.0);

    // Get storage location of u_ModelMatrix
    var u_ModelMatrix = gl.getUniformLocation(gl.program, 'u_ModelMatrix');
    if (!u_ModelMatrix) {
      console.log('Failed to get the storage location of u_ModelMatrix');
      return;
    }

    // Current rotation angle
    var currentAngle = 0.0;
    // Model matrix
    var modelMatrix = new Matrix4();

    // Start drawing
    var tick = function() {
      currentAngle = animate(currentAngle);  // Update the rotation angle
      draw(gl, n, currentAngle, modelMatrix, u_ModelMatrix);   // Draw the triangle
      requestAnimationFrame(tick, canvas); // Request that the browser calls tick
    };
    tick();
  }

  function initVertexBuffers(gl) {
    var vertices = new Float32Array ([
      0, 0.5,   -0.5, -0.5,   0.5, -0.5
    ]);
    var n = 3;   // The number of vertices

    // Create a buffer object
    var vertexBuffer = gl.createBuffer();
    if (!vertexBuffer) {
      console.log('Failed to create the buffer object');
      return -1;
    }

    // Bind the buffer object to target
    gl.bindBuffer(gl.ARRAY_BUFFER, vertexBuffer);
    // Write date into the buffer object
    gl.bufferData(gl.ARRAY_BUFFER, vertices, gl.STATIC_DRAW);

    // Assign the buffer object to a_Position variable
    var a_Position = gl.getAttribLocation(gl.program, 'a_Position');
    if(a_Position < 0) {
      console.log('Failed to get the storage location of a_Position');
      return -1;
    }
    gl.vertexAttribPointer(a_Position, 2, gl.FLOAT, false, 0, 0);

    // Enable the assignment to a_Position variable
    gl.enableVertexAttribArray(a_Position);

    return n;
  }

  function draw(gl, n, currentAngle, modelMatrix, u_ModelMatrix) {
    // Set the rotation matrix
    modelMatrix.setRotate(currentAngle, 0, 0, 1); // Rotation angle, rotation axis (0, 0, 1)
    modelMatrix.translate(0.35, 0, 0)
    // Pass the rotation matrix to the vertex shader
    gl.uniformMatrix4fv(u_ModelMatrix, false, modelMatrix.elements);

    // Clear <canvas>
    gl.clear(gl.COLOR_BUFFER_BIT);

    // Draw the rectangle
    gl.drawArrays(gl.TRIANGLES, 0, n);
  }

  // Last time that this function was called
  var g_last = Date.now();
  function animate(angle) {
    // Calculate the elapsed time
    var now = Date.now();
    var elapsed = now - g_last;
    g_last = now;
    // Update the current rotation angle (adjusted by the elapsed time)
    var newAngle = angle + (ANGLE_STEP * elapsed) / 1000.0;
    return newAngle %= 360;
  }
  main()
}()
